This invention relates to a method of forming fins on a strip. This fin strip is then inserted into a flat tube for a heat exchanger and brazed.
Conventionally, there are three methods of forming a corrugated plate from a strip with rollers. The first method is shown in FIG. 13. A strip 60 is advanced by rotation of plural pairs of rollers, including upper rollers 31 and 33 and lower rollers 32 and 34, so that a fin 61 is gradually formed on the strip 60.
The upper rollers 31 and 33 have protrusions 31a and 33a which protrude radially with respect to the axis of rotation along their circumferences and the lower rollers 32 and 34 have matrix depressions 32a and 34a which mate with the protrusions 31a and 33a through clearances along their outer circumferences. The thickness of the strip is almost the same before and after the process.
The second method of forming such a plate is shown in FIG. 14. An upper roller 41 and a lower roller 42 having a plurality of protrusions vary the thickness of the strip 60 in the direction of width with one or two steps of the process so that fins 62 are formed on the strip 60. This method is disclosed in Japanese patent application laid open (KOKAI)62-212025.
The third method is shown in FIG. 15. The strip 60 is put between gears 51 and 52 which have almost the same length as the width of the strip 60 so that a corrugated plate is formed at one time. This method is disclosed in Japanese patent application laid open (KOKAI)43-29307.
However, each of the above methods have their own defects. In the first method, the number of paired upper and lower rollers become large so that the number of steps of the manufacturing process increases. In the second method, tensile stress beyond the yield stress is applied to cause residual extensional deformation so that a corrugated plate is formed. However, to form accurate corrugations with a flat plate having equal thickness is generally completed only when a sine wave corrugation having low height against the pitch of the wave is required. If the rectangular corrugation is required, the corrugated plate partially loses its thickness and may rupture. In the third method, if the length b of fins 63 in FIG. 15 is required to change a strip 60 which has a width to cover the change and further rollers 51 and 52 which have a length to cover the change are required so that flexibility for responding variation of fin length b becomes small.
The object of this invention is to provide a method of forming fins which makes a manufacturing process simple, which does not cause the strip to be ruptured at the time of process and which easily obtains production having requested length.